1. Field of the Invention
The present invention relates to a method of manufacturing a cathode ray tube, and particularly to a baking method used in the case of forming a phosphor coating, an acrylic resin layer and a metallization layer on the inner surface of the panel of a cathode ray tube, and then baking and decomposing polyvinyl alcohol (PVA) contained in the phosphor coating and the acrylic resin. This invention is also concerned with a ventilator used in the above baking process.
2. Description of the Prior Art
According to a prior art method of manufacturing a color cathode ray tube, at first, on the panel inner surface of the cathode ray tube there is uniformly coated phosphor slurry composed of phosphor and a photosensitive binder (including PVA). After drying the above slurry, a process of exposing and developing it in a predetermined pattern is repeated at every color to produce a color phosphor coating consisting of, for example, green, blue and red color phosphor stripes. Next, on this color phosphor coating there is coated a water emulsion of acrylic resin which serves as a priming for forming a flat metallization layer. After being dried, this acrylic resin layer is applied thereon with a metallization layer consisting of a vaporized film such as aluminum. Then, this panel portion and a funnel portion, which integrally includes a neck portion, are placed in a frit-sealing furnace with a mutually coupled condition and frit-sealed together to produce a bulb. In this process, the frit-sealing operation between panel portion and funnel portion is carried out and also organic substances in the tube such as PVA in the phosphor coating and acrylic resin are subjected to baking and decomposing operation. With the above processes, a color cathode ray tube is manufactured.
Recently, in order to increase the brightness of a cathode ray tube, there has been proposed a method of forming a phosphor coating by using phosphor having large grain size (so-called non-ballmilled phosphor), and accordingly, a new type acrylic resin layer has been required from a viewpoint of coating technique. In coating this acrylic resin layer, since the phosphor is large in grain size, it is necessary to increase the concentration of acrylic resin in water emulsion (new concentration is 34 to 40%, while the prior concentration has been 25%), and is also necessary to make the film a little thick. However, when such phosphor with large grain size is employed, it was ascertained that with the prior art manufacturing method as mentioned above, or with the processes including the formation of phosphor coating, the formation of the metallization layer, the coupling of the panel portion and the funnel portion, the frit-sealing process, and the like, the PVA and acrylic resin are not fully decomposed and hence, an object to use a new phosphor is not attained. In the prior art, the above problem has been settled by using the combination of processes that form the metallization layer, only the panel is pre-baked. Then the panel portion and funnel portion are combined to be frit-sealed, but at present they cannot be completely decomposed and removed as organic gas. This is considered to be caused by a fact that the tube passes through the furnace with the shape of a bulb having a narrow neck portion so that the inside of the bulb is not ventilated and an atmosphere necessary for baking and decomposing the phosphor surface can not be obtained.